As Brucelee points out, there are two things that cause excessive wear on the engine. Excessive loads on the connecting rods and crankshaft and inadequate lubrication. At sustained high revs the rings tend to dry out causing excessive wear. At extremely low revs (below 2000) the loads on the rods and crank can exceed available lubrication also causing excessive wear.
Excessive heat will also cause rapid wear.
These motors were designed to use the entire rev range with momentary revs above 5000. As long as you are running through the gears your lubrication has time to catch up and replenish the rings without excessive wear. Sustained revs above 5000 or below 2000 with high loads on the motor will tend to cause excessive wear.
So what should you do to keep your motor in good health? Under normal street driving keep your car in the midrange between 2-4 k for best lubrication, cooling and lowest engine loads. Use low revs below 2k only when there is little or no load on the motor (flat ground or downhill). Use the upper range 4-6k for spirited runs and track use, shifting up when needed to avoid sustained revs above 5k. Change your oil and air filter more often.
